This invention is in the field of diagnostics in radiography and radioimaging and is more particularly concerned with a composition and method of preparing the composition for use in scintigraphy.
For most patients with solid tumors, the most powerful and predictive prognostic factor of survival is the status of regional lymph nodes (Albertini et al. (1996); Cox C. (1998); De Cicco et al. (1997); Reintgen and Conrad (1997)). Hence it remains important to identify those patients with nodal involvement in order to differentiate those patients who will clearly benefit from systemic treatment. The sentinel node is that lymph node in a given lymphatic basin that first receives lymphatic flow from a primary tumor (Gulec et al. (1997)). As a result the histology of the sentinel node usually reflects the histology of the basin. Therefore, if there is cancer in the sentinel node, there may be metastatic disease in other nodes, but, if the sentinel node is cancer-free, there is greater than 98% likelihood that the remaining nodes in the basin are negative. Thus, the sentinel node is the best tissue to sample for histophathologic examination (Alazraki et al. (1997)).
Sentinel node lymphoscintigraphy (SNL) has made it possible to perform complete lymph node dissection only in those patients with confirmed nodal metastasis. SNL therefore reduces the surgical morbidity associated with such a procedure including: parasthesia, wound infection, seroma, drain discomfort, acute and chorin lymphodema, as well as potential delays in adjuvant therapy (Cox (1998); Hinkle (1998)). Furthermore, lymphatic mapping and sentinel node biopsies direct dissection to all lymph node beds that could have tumors. Not infrequently, a sentinel lymph node that shows micrometastasis is in a lymph node bed that would not have been predicted to receive lymphatic drainage from the primary tumor based on conventional estimates (Alazraki et al. (1997)). The classic concept of a lymphatic watershed described by Sappey""s line (an anatomic coordinate governing the direction of lymphatic flow from any point on the trunk) has been shown by lymphoscintigraphy to be erroneous (Ege G: Lymphoscintigraphy in Oncolgy. Chapter 94 Nuclear Medicine Volume II. Mosby Year Book, St. Louis, Mo. 1504-1523).
The procedure involves injecting radiopharmaceuticals (specifically radiolabeled colloid of suitable size and properties) at the primary tumor site, which allows the path of lymphatics, for example from a cutaneous melanoma or breast lesion, to the regional node basin to be traced. Using the nuclear images as a road map, gamma probe guided surgery (with a hand-held, wand-like instrument that detects gamma rays emitted by the radiocolloid) successfully locates the sentinel node, allowing a directed dissection and minimizing tissue disruption (Alazraki (1998); Pijpers et al. (1995)). The fact that only one or two nodes need examination makes it possible for the pathological investigation to apply techniques such as immunohistochemical staining and PCR-based assays which are more sensitive than routine HandE staining for detecting micrometastasis (Guiliano et al. (1997); Reintgen and Conrad (1997)).
Technetium-labeled sulfur (Tcxe2x80x94S) colloids have been used for years to image the reticuloendothelial system. There are three reported methods of making such preparations:
(1) 99mTcOxe2x88x924+H2S in acid solution;
(2) 99mTcOxe2x88x924+Sb2S3 colloid in acid, and
(3) 99mTcOxe2x88x924+Na2S2O3+acid.
The major commercial source of Tcxe2x80x94S colloid preparations is the reaction mixture formed from pertechnetate-99m in an acidified solution of sodium thiosulphate (Atkins, H. L., et al. (1966); Stern H. S., et al. (1966)). Such standard preparations result in a final pH on average of between 5.0 and 6.5. Such pH values cause significant irritation in patients often requiring a local anesthetic to accompany the injection.
There are several desirable characteristics of the ideal radiocolloid for use in SNL including ease of labeling; sutiable half life and energy characteristics; permitting quantitative or dynamic measurement and high quality imaging; ease of preparation and good shelf life; physiologically and chemically inert and homogeneous; sterility and pyrogenicity readily established via Quality Control procedures; in vitro and in vivo stability; and optimal mobilization of colloid from injection site. However the rate of colloid transport and movement through lymphatic pathways is most strongly related to the size of the colloid. Those larger than 0.004 xcexcm to 0.005 xcexcm are preferred, as smaller particles have been reported to penetrate the capillary membranes and are therefore unavailable to migrate through the lymphatic channels resulting in obscured images. Particles smaller than 0.1 xcexcm show the most rapid disappearance from the interstitial space into the lymphatic vessels and have significant retention in the lymph node. Large colloid particles (xcx9c0.5 xcexcm) show a much slower rate of clearance from the interstitial space with significantly less accumulation in the lymph nodes (Alazraki et al. (1997); Bergqvist et al. (1983); Ege G: Lymphoscintigraphy in Oncolgy. Chapter 94 Nuclear Medicine Volume II. Mosby Year Book, St. Louis, Mo. 1504-1523; Eshima et al. (1996); Hung et al. (1995); Nagai et al. (1982)).
Several reports indicate that the physico-chemical properties of these colloids influence the efficiency of their phagocytosis (Dobson (1957; Neukomm et al. (1957); Scott et al. (1967); Atkins et al. (1970)), and some investigators have described anomalies in the behaviour of sulfur colloid (Chaudhuri and Evans (1973); Haiback et al. (1975); Bradfield and Wagner (1977)).
The present inventors have developed a new formulation of Tc-99m colloid. The new colloid contains a high ratio of perrhenate to thiosulphate, cysteine, and a prepared higher final pH than found previously. As used herein, a xe2x80x9cfinal pHxe2x80x9d means the pH of the final formulation and can be between about 5.5 and about 8.0, but is preferably between about 7.0 and about 7.5. Also, as used herein, xe2x80x9chigh ratioxe2x80x9d means from about 0.05 to about 1.2 rhenium:sulfur and in any event, less than rhenium and no sulfur. In addition, the new colloid has excellent radiochemical purity, and a much smaller particle size distribution than has generally been previously available for sulfur colloid preparations.
Accordingly, the present invention provides a colloid particle, containing a high ratio of rhenium to sulfur, and containing a source of sulfhydryl groups (xe2x80x94SH), and technetium, preferably wherein the particle is less than about 0.1 micron in diameter and the technetium is Tc-99m.
The invention also provides a colloid containing a high ratio of rhenium to sulfur, and containing a source of xe2x80x94SH, and technetium wherein a majority of the particles, preferably greater than about 80% of the particles, of the colloid, are less than about 0.1 micron in diameter and the technetium of these particles is Tc-99m.
According to another aspect, the invention provides a method of preparing a colloid containing a high ratio of rhenium to sulfur, and containing a source of xe2x80x94SH, and technetium comprising the steps of: in a container adding a source of sulfur and a source of rhenium; adding a source of technetium; before boiling adding a source of xe2x80x94SH; acidifying the contents of the container; boiling the contents of the container; cooling the contents of the container; raising the pH of the contents of the container to a higher final pH between about 5.5 to about 8.0, preferably between about 7.0 and about 7.5.
Also provided is a method of detecting sentinel lymph node(s) associated with a tumor comprising administering a sufficient amount of a radiopharmaceutical colloid according to the present invention to an animal, detecting radiation emitted from the animal, and correlating the emissions to locate the associated sentinel lymph node(s).